1. Field of the Invention
The present invention relates to a bone prosthetic material (filler) which is useful in oral surgery, orthopedic surgery and other fields for the purpose of filling the part of a bone which has been removed such bone removal may result from an operation on bone tumor, pyorrhea alveolaris or other diseases. The present invention also relates to a process for producing such a bone prosthetic material.
2. Background of the Invention
Bone prosthetic materials of the type contemplated by the present invention have heretofore been used in the form of blocks, granules or some other shapes that are formed of metals (e.g., cobalt-chromium alloys, titanium, and stainless steel), ceramics (e.g., alumina, zirconia, tricalcium phosphate, hydroxyapatite, and calcium phosphate-based glass), high-molecular weight materials (e.g., silicone resins) and carbon.
Of these materials, those which are based on a calcium phosphate group such as tricalcium phosphate, hydroxyapatite and calcium phosphate-based glass have been the subject of the most intensive studies in recent years because they are very similar to bones in composition and exhibit an extremely high degree of biocompatibility. However, even bone prosthetic materials made of such calcium phosphate group based materials are "foreign" to living tissues and their ability to coalesce with a new growth of bone is limited to the area which is close to the living tissues of interest. In areas distant from such living tissues the prosthetic material is subjected to a so-called encapsulating reaction in which the prosthetic material is surrounded by fibrous tissue and becomes excessively soft. Therefore, in areas where the healing process is inactive, even the bone prosthetic materials made from calcium phosphate materials fail to display good biocompatibility with the body tissues because of their encapsulation in a fibrous tissue.
Unexamined Published Japanese Patent Application No. 21763/1985 discloses an artificial bone material that is composed of sintered hydroxyapatite having open cells with sizes of 10-100 .mu.m and a flexural strength of at least 100 kg/cm.sup.2. However, this artificial bone material has to sacrifice the porosity in order to attain a flexural strength of at least 100 kg/cm.sup.2, and the number of open cells it has is too small to effectively prevent encapsulation in a fibrous capsule.